This invention relates in general to wells that produce gas and condensate and in particular to a heater cable deployable while the well is live for raising the temperature of the gas being produced to reduce the amount of condensate.
Many gas wells produce liquids along with the gas. The liquid may be a hydrocarbon or water that condenses as the gas flows up the well. The liquid my be in the form of a vapor in the earth formation and lower portions of the well due to sufficiently high pressure and temperature. The pressure and the temperature normally drop as the gas flows up the well. When the gas reaches or nears its dew point, condensation occurs, resulting in liquid droplets. Liquid droplets in the gas stream cause a pressure drop due to frictional effects. A pressure drop results in a lower flow rate at the wellhead. The decrease in flow rate due to the condensation can cause significant drop in production if quantity and size of the droplets are large enough. A lower production rate causes a decrease in income from the well. In severe cases, a low production rate may cause the operator to abandon the well.
Applying heat to a well by the use of a downhole heater cable has been done for wells in permafrost regions and to other wells for various purposes. In one technique in permafrost regions, the production tubing is pulled out of the well and a heater cable is strapped onto the tubing as it is lowered back into the well. One difficulty with this technique in a gas well is that the well would have to be killed before pulling the tubing. This is performed by circulating a liquid through the tubing and tubing annulus that has a weight sufficient to create a hydrostatic pressure greater than the formation pressure. In low pressure gas wells, killing the well is risky in that the well may not readily start producing after the killing liquid is removed. The kill liquid may flow into the formation, blocking the return of gas flow.
Another problem associated within the use of heater cable is to avoid loss of the heat energy through the tubing annulus to the casing and earth formation. This lost heat is not available to increase the temperature of the produced gas and significantly increases heating costs. It is also known to thermally insulate at least portion s of the production tubing in various manner to retard heat loss.
In this invention a method of heating gas being produced in a well is provided to reduce condensate occurring in the well. A cable assembly having at least one insulated conductor is coiled on a reel and transported to a well site. The cable assembly is deployed from the reel into the well while the well is still live. A pressure controller is preferably used at the upper end of the production tubing to install the cable while the well is live. Electrical power is supplied to the conductor to cause heat to be generated. Gas flows up past the cable assembly and out the wellhead.
Preferably, there is a plurality of conductors in the cable, and the lower ends are secured together. Also, preferably, the cable is contained within a coiled tubing. Heat transfer from the cable may be increased by providing a dielectric liquid in the tubing annulus, by drawing a vacuum in the tubing annulus, or by applying heat reflective coatings to the tubing and/or the casing. The cable may be divided into sections, with some of the sections providing more heat than others.